The BepiColombo Mercury Planetary Orbiter Mechanical and Propulsion Bus Proto-Flight Model (the structure with integrated heat pipes and chemical propulsion subsystem) has been baked out in the Phenix thermal vacuum facility at ESA's European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands.

The BepiColombo Mercury Planetary Orbiter (MPO) Mechanical and Propulsion Bus (MPB) Proto-Flight Model (PFM) has been baked out in the Phenix thermal vacuum facility at ESA's European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands. T

This process involved heating the MPB to 60C in a vacuum for 20 days to remove any contaminants that would outgas in space.

Given the extremes of temperature to which BepiColombo will be exposed - in excess of 350C on the parts illuminated by the Sun, -120C or less on the parts exposed to cold space - prevention of outgassing is important because the outgassing products from the hot areas of the spacecraft may recondense on colder areas or be photochemically deposited on Sun-illuminated surfaces by ultraviolet radiation.

Contamination of thermal control surfaces would alter their absorptivity / emissivity ratios, possibly causing an uncontrolled increase in temperature.

Contamination of the solar arrays could greatly decrease their power output, while contamination of the instruments would severely degrade their optics. Molecular contamination is caused by volatiles that are released by materials such as paints, plastics and adhesives.

The Phenix thermal vacuum facility is designed for small and medium spacecraft and subsystems. The facility consists of a cylindrical vacuum chamber nearly 12 metres long and 4.5 metres in diameter, with access gained through a 4.5-metre-diameter door. The chamber is equipped with a movable box-shaped shroud system and a movable platform on which the test item is mounted.

This design enables a quicker throughput time as the movable platform and shroud enable preparation outside the chamber and rapid loading of the facility. Phenix typically achieves a vacuum of 5 + 10-6 millibar in the absence of heavily outgassing materials.

The MPB PFM will now be transported to Thales Alenia in Turin for integration of additional equipment and subsystems. These have already been subjected to a similar outgassing treatment.